170 
IDDINGS. 
tion of the general magma with which they are associated.* 
But in the lava flows which were erupted near the end of 
the volcanic action wdiich produced these extreme varieties 
of rocks and which lie immediately beneath the ejectamenta 
of a later series of eruptions, there occur varieties which 
correspond to the extreme forms of the dike rocks. The 
correspondence is partly in chemical composition and partly 
in mineral composition and habit, and also in association. 
There are three localities in which the surface equivalents 
of these exceptional rocks have been observed. One is near 
the Crandall and Stinking Water centers, on the high peaks 
between Lamar river and a northwest branch of Stinking 
Water river. The surface flows are basaltic in character, 
carrying phenocrysts of olivine and augite and sometimes 
plagioclase. In one instance the groundmass consists of 
alkali feldspars with leucite, and the chemical composition 
of the rock, analysis 12, Table III, shows its similarity to 
other flows to be mentioned, and to the minette, analysis 7. 
Associated with and overlying these alkali basalts is a small 
fragment of sanidine-mica-rock, which is the equivalent of 
the syenite-porphyry or oligoclase-porphyrite of the dikes. 
Other orthoclase basalts form flows farther west and have 
similar chemical compositions, analyses 5 and 8. 
A second occurrence is on a branch of Beaverdam creek, 
a short distance southeast of the Yellowstone lake. Here 
there are two sheets of alkali basalt, one of which is a leu- 
cite-orthoclase-basalt or basanite, and the other an alkali- 
plagioclase-basalt. The chemical composition of these rocks 
is shown by analyses 14 and 15. The leucite rock is the 
younger of the two. This rock, analysis 14, has nearly the 
same composition as the minettes, whose analyses are Nos. 
7 and 10. The second rock, an alkali-plagioclase-basalt, 
analysis 15, is closely related in composition to the ortho- 
clase-basalt-flows, but corresponds more nearly to the mica- 
augite-andesite, analysis 16. 
* Rosenbusch (H.) Mikro. Phys. d. Mas. Gest. 8°. Stuttgart, 1886, 
vol. II, p. ix; alsb “Ueber Monchiquite,” etc. Min. u. petr. Mitth. 8°. 
Vienna, 1890, vol. 11, p.31. 
